Photoacoustical apparatus



July 18, 1939. J, QBAKER 2,166,672

PHOTOACOUSTICAL APPARATUS Filed Feb. 29. 1936 INVENTOR c/UDD O. BAKE? ATTORNEY Patented July 18, 1939 UNITED STATES PHOTOACOUSTIGAL APPARATUS Judd 0. Baker, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application February 29, 1936, Serial No. 66,337

8 Claims.

This invention relates to photo-acoustical apparatus wherein the recorded vibrations are reproduced by the use of a photoelectric device, and more particularly to the photoelectric device itself.

Photographic sound records may be broadly divided into two classes one of which is known as the variable area type and the other the variable density type. Each of these may be further subdivided into records wherein the sound impressions are formed as a single full wave track or a series of such tracks in phase and into records wherein the sound impressions are formed as two half wave tracks either 180 out of phase or in phase. The former type is illustrated, for example, by the Hart Patent, No. 1,588,886 in Figure 5 of which is shown a single full wave track of the variable area type, while the patent to Neale, No. 1,879,423, illustrates the second 20 type, showing a variable area record of two half Wave tracks in Figure 2 and showing a variable density record of two half wave tracks in Figure 4, each of the latter tracks having half waves 180 out of phase. With records having single 25 full wave tracks, a photoelectric cell having a single cathode and a single anode may be used, the photoelectric cell being coupled to a single ended amplifier. Such a reproducing system is commonly known as and, for the sake of con- 00 venience, will hereinafter be referred to as the standard system. With records having two half wave tracks 180 out of phase or in phase,

however, a photo-electric cell having two cathodes and either one or two anodes must be used,

6 this cell being coupled to an amplifier of the push-pull type.

Heretofore, so far as I am aware, there has been no single reproducing system with which records of either type could be satisfactorily 40 reproduced. The practice heretofore has been to change photocells to correspond with the particular type of record used, and this has, of course, necessitated changing amplifier connections, and in some cases even the amplifier circuit itself, or a difierent amplifier was used with each photocell.

The primary object of my invention is to provide an improved reproducing system which will reproduce sound satisfactorily from either type of record above described.

More specifically, it is an object of my invention to provide an improved reproducing system which can be easily and quickly converted from a standard to a push-pull system and vice versa by -a mere simple manipulation.

Another object of my invention is to provide an improved photoelectric cell which is suitable for reproduction of sound from either a record having a single full wave sound track or from a record having a track wherein the sound is represented by two half waves 180 out of phase.

A further object of my invention is to provide an improved photoelectric cell of the type specified which is simple in construction and highly efficient in use.

In accordance with my invention, I provide a photo-electric device having a glass envelope in which is enclosed two sets of electrodes, one set having a single cathode and a single anode and being adapted for use in a standard system, and the other set having two cathode and either one or two anodes for joint operation in a push-pull system. Each of these electrodes is connected to a terminal member at the base of the tube by means of which the tube may. be coupled to the input transformer of a suitable amplifier, the transformer having two primaries in series which may both be coupled to the single set of electrodes of the photoelectric device so that both primaries will cooperate therewith when standard operation is desired, or which may be coupled thereto so that one cooperates with only one of the two joint operable pairs of electrodes and the other with the second of the two jointly operable pairs of electrodes when push-pull operation is desired. Proper connection of the two transformer primaries with the tube terminals is automatically effected by either shifting the phototube rectilinearly or rotating it 180 depending upon the manner in which the various electrodes are disposed therein. Thus, by a simple manipulation, the same equipment may be conditioned for either standard or push-pull reproduction.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of two embodiments thereof when read in connection with the accompanying drawing in which Figure 1 is a diagrammatic view of one form of phototube in accordance with my invention and connected to the input transformer of an amplifier for push-pull reproduction.

Figure 2 is a similar view of a modified form of phototube built in accordance with my invention, and

Figure 3 is a diagrammatic View of the latter form of phototube coupled to the input transformer for standard reproduction.

Referring more in detail to the drawing, wherein similar reference characters designate corresponding parts through-out, there is shown, in Figure 1, a photoelectric device comprising an elongated envelope I housing a plurality of cathodes 3, 5 and 1 with which are cooperatively associated, respectively, the anodes 4, 6 and 8. The electrodes 3 and 4 are longitudinally displaced from the two pairs of electrodes 5, 6 and 1, 8 and are located on one side of a medium plane 9 passing through the envelope I, while the electrodes 5, 6 and 1, 8 are located on the other side of the plane 9. The electrodes 3 and 4 are respectively connected to external connectors or terminal members II and I2, while the electrodes 5, 6, 1 and 8 are respectively connected to terminal members I3, I4, I5 and I6, and by means of these terminal members, the photoelectric device may be coupled not only to the input transformer I1 of a suitable amplifier with respect to whichthe photoelectric device is movable recti linearly in the directions indicated by the arrow heads A and B, but also to a source of potential I9. The photoelectric device is also provided with a pair of terminal members 2|, 23 bridged by a conductor 22, and a second pair of terminal members 25, 21 bridged by a conductor 25.

The transformer I1 comp-rises two primary coils P1 and P2 which may be coupled in series either by the terminal members 2I, 23 and their bridge 22 or by the terminal members 25, 21 and their bridge 26, depending upon whether the photoelectric device occupies the position with respect to the transformer I1 shown in Figure 1 or whether it has been moved in the direction of the arrow head A to another predetermined position to be more fully set forth presently. The two pairs of electrodes 5, 6 and 1, 3 constitute a set of jointly operable pairs of electrodes adapted for use with a sound record of the type shown in the Neale patent heretofore identified, and when coupled to the transformer I1 as shown in Figure 1, the system is conditioned for push-pull operation, If the sensitivity of the two cathodes 5 and 1 is not the same, as is frequently the case, the potential across the electrodes 5, 6 and 1, 8 may be adjusted to compensate for this difference in sensitivity to compensate by means of a biasing resistor 29 grounded at each end and a variable tap 3|, the terminals 14 and It being respectively connected to fixed taps on the resistor 29 by conductor leads 34 and 35. In operation, light from a suitable source 38 is intercepted and modulated by a photographic record or other suitable light intercepting medium (not shown) :and thereafter focused on to the cathodes 5, 1 by a pair of adjacent lenses 39, one of which cooperates with the cathode 5 and the other of which cooperates with the cathode i. During one half cycle, light from the source 33 may impinge upon the cathode 5, in which case current is varied in the circuit formed by ground, the battery I9, the variable tap 3|, that portion of the biasing resistor 29 between the variable tap 3| and the lead 34, the lead 34 and terminal member I4, the anode 6, the cathode 5, conductor 35, terminal member I3, conductor 31, primary P1, conductor 40, terminal member 23, bridge 22, terminal member 21, and conductor 4| and ground. During the other half cycle, light from the source 28 impinges upon the cathode 1, whereupon current is varied in the circuit extending from ground through the battery I9, the variable tap 31, that portion of the resistor 29 between the variable tap 3| and the lead 36, the lead 36, terminal member IS, the anode,8, the cathode 1, conductor 43, terminal member I5, conductor 45, primary P2, and conductor 41 to ground. In this manner, reproduction may be satisfactorily obtained from a record of which the sound track is in the form of two half cycles out of phase or in phase.

When it is desired to reproduce sound from a full wave, single track record of the type shown in the Hart patent identified above, the photoelectric device is moved in the direction of the arrow head A to a position such that the terminal member I2 engages a conductor 49, the terminal member 25 engages the conductor 45, the terminal member I I engages the conductor 31, and the terminal member 21 engages the conductor 40, a lens 5| being arranged to move with the photoelectric device into the path of light from the source 31 to occupy the position formerly occupied by the lenses 39. In this case, light from the source 38 is modulated by the photographic record or other suitable light intercepting medium and, by means of the lens 5|, is focused on the cathode 3, and current is varied in a circuit extending from ground through the battery I9, the lead 49, the terminal member I2, the anode 4, the cathode 3, the terminal member I I, the conductor 31, the primary P1, the conductor 40, the terminal member 21, the bridge 26, the terminal member 25, the conductor 45, the primary P2, and the lead 41 to ground. It will be seen, therefore, that by the simple manipulation of moving the photoelectric device either in the direction of the arrow head A or the direction of the arrow head B, the system can be at once properly conditioned to reproduce sound from either one or the other of the two types of sound records heretofore described In Figures 2 and 3, I have shown a modified form of photoelectric device, the envelope I in this case being cylindrical and the electrodes 3, 4 being circumferentially displaced 180 from the jointly cooperable pairs of electrodes 5, 5 and 1, 8, so that it is necessary to rotate the photoelectric device through that angle in order to condition the system for reproduction from one type of record or the other. Also, there is shown in Figures 2 and 3 an opaque cylindrical guard 53 which may be placed around the transparent envelope I and in which the lenses 39, 39 and 5| may be mounted, the guard 53 serving to prevent stray light from reaching the light-sensitive cathodes 3, 5, and 1, and a similar guard may be used in connection with the form of my invention shown in Figure 1. In all other respects, however, the modification shown in Figures 2 and 3 is similar to that shown in Figure 1, including all circuit connections thereto heretofore described in detail, Thus, if it is desired to transform the system from push-pull to standard, it is merely necessarly to rotate the photoelectric device and the guard 53, which is rigidly associated therewith, 180 in the direction of the arrow head B to provide the connections shown in Figure 3. On the other hand, to recondition the system for push-pull reproduction, the assembly is rotated 180 in the direction indicated by the arrow head A to provide the circuit connections shown in Figure 2.

Although I have shown and described my invention in considerable detail, I am fully aware that many modifications thereof and changes therein may be made within its scope. I desire, therefore, that my invention shall not be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In photo-acoustical apparatus, the combination of an amplifier adapted for either standard operation or for push-pull operation, and a photoelectric device associated therewith, said photoelectric device having a plurality of sets of cooperative electrodes therein of which certain sets are arranged to act jointly in pairs for push-pull operation and of which another set is arranged to act independently of said certain sets for standard operation, and means whereby said photoelectric device may be coupled to said amplifier to provide either a standard reproduc ing system or a push-pull reproducing system at will.

2. In a photo-acoustical apparatus, the combination of an amplifier adapted for either standard operation or for push-pull operation, and a photo-electric device movably associated therewith, said photoelectric device having a plurality of set of cooperative electrodes therein of which certain sets are arranged to act jointly in pairs for pu s-pull operation and of which another set is arranged to act independently of said certain sets for standard operation, and means whereby, upon movement of said photo-electric device to one of two predetermined positions relative to said amplifier, said jointly acting sets of electrodes will be coupled to said amplifier to provide a push-pull reproducing system, and upon movement of said photoelectric device to the other of said two predetermined positions, said other sets of electrodes will be coupled to said amplifier to provide a standard reproducing system.

3. The invention set forth in claim 2 characterized in that said jointly acting sets of electrodes are longitudinally spaced from said other set of electrodes, and characterized also in that said photoelectric device is movable rectilinearly between said two predetermined positions.

t. The invention set forth in claim 2 characterized in that said jointly acting sets of electrodes are spaced circumferentially from said other set of electrodes, and characterized also in that said photoelectric device is rotatable between said two predetermined positions.

5. The invention set forth in claim 2 characterized in that said amplifier includes an input transformer having two series connected primaries, and characterized further in that when said photoelectric device is moved to the first of said two predetermined positions, one pair of said jointly acting pairs of electrodes becomes coupled to one of said primaries and the other pair of said jointly acting pairs of electrodes becomes coupled to the other of said primaries, and when said photoelectric device is moved to the other of said two predetermined positions, said other set of electrodes becomes coupled to both of said primaries.

6. In combination, a photoelectric device having two cathodes of different sensitivities and two anodes, one of said cathodes being associated with one of said anodes to constitute one pair of cooperab-le electrodes, and the other of said cathodes being associated with the other of said anodes to constitute a second pair of cooperable electrodes, means for providing a potential across each of said pairs of electrodes, and means for adjusting the potential across each of said pairs of electrodes whereby to compensate for the diiTerence in sensitivity of said cathodes.

'7. In combination, a photoelectric device having two cathodes of diiierent sensitivities and two anodes, one of said cathodes being associatcd with one of said anodes to constitute one pair of cooperable electrodes, and the other of said cathodes being associated with the other of said anodes to constitute a second pair of coop-- erable electrodes, means in circuit with said electrodes for providing a potential across each of said pairs of electrodes, and a balancing resistor in said circuit for adjusting the potential across each of. said pairs of electrodes whereby to compensate for the differences in sensitivity of said cathodes.

8. The invention set forth in claim 2 characterized by the addition of a light source and two sets of lenses one of which is adapted for operation with a plural track record and the other of which is adapted for operation with a single track record, said lenses being mounted for movement simultaneously with said photoelectric device and being so arranged that when said photoelectric device is moved to the first of said predetermined positions, said first named set of lenses will be positioned in the path of light from said light source and when said photoelectric device is moved to the other of said predetermined positions, said second named lens will be positioned in said light path.

JUDD O. BAKER. 

